MO drives use magneto-optical technology to provide high-capacity portable media for computers. They use a laser and magnetic head to read and write to MO diskettes, which are twice as thick as floppy disks. The Kerr effect is used to read the disk, while the Curie point is used to write. MO drives are durable and have large capacity, but their use has declined since 2000. They are still used for data storage tasks where multiple disks can be placed within an enclosure with one or two drives.
An MO drive is a type of disk drive that uses magneto-optical (MO) technology to provide high-capacity portable media for computer systems. The drive itself uses two separate processes to read and write to an MO diskette, a laser and a magnetic head. Where the laser is used to both read and write to the media, the magnetic head is only for writing. As a result, the special media used with an MO drive can provide extremely long life and very reliable, high-capacity data storage.
The disks for an MO drive look a lot like typical floppy disks, but are about twice as thick. Inside the floppy disk case, the disk platter is composed of a thin layer of ferromagnetic material bonded within a plastic liner. This material acts much like a platter inside a hard disk drive in that there are tracks with tiny sectors magnetized in a positive or negative state to represent ones or zeros for the digital data stored on the disk. Disks can be formatted using any number of disk file systems and, when inserted into the MO drive, are seen by a computer’s operating system as just another disk drive.
Inside the MO drive, a small sliding door is opened on the floppy and the platter is positioned between the drive’s laser on the bottom and the magnetic head suspended above. As the platter spins to read the disk, the laser is set to low power and the beam bounces off the disk’s sectors according to their magnetic state. This is a process known as the Kerr effect. When the laser beam hits a positive magnetic state, or “one,” the beam bounces back in one direction, and when it hits a negative magnetic state, a “zero,” it bounces back in the opposite direction. The drive then ascertains the contents of the disc by observing the laser return.
When an MO drive wants to write to a disc, it has to increase the laser power to heat up the ferromagnetic material of the platter. The laser heats the material to what is called its Curie point, the temperature at which it can be affected by magnetic fields. Once a sector has been heated, it can be written to by the magnetic head on the opposite side of the diskette, which gives a heated sector a positive or negative state. The floppy platter must make two passes through the drive for the writing process to complete, doubling the time it takes to write data with an MO drive compared to simply reading. Of course, this process is infinitely repeatable on an MO drive and a floppy disk, making them infinitely rewritable without having to reformat the floppy every time as with traditional floppy drive media.
In many Western countries, the use of MO drive technology has declined slightly since around the year 2000, although they still find use in specific areas. Due to the durability and large capacity of the disks, MO drives are also used for many data storage tasks, where a number of MO disks can be placed within an enclosure with one or two drives requiring the disks through robotic arms. A server running special software checks requests to the data library and organizes the data across multiple disks.
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